1. Field of the Invention
This invention relates in general to an electrical capacitor which is formed of electrical foil particularly a wound electrolytic capacitor for high alternating current loads which is mounted in a metallic housing and has a metallic heat bridge between the capacitor and the housing which is formed by an electrode foil that overlaps an end face at one end and is in thermal contact with the floor of the housing at the other end.
2. Description of the Prior Art
Wound electrolytic capacitors are generally formed of an anode foil of aluminum which is provided with a dielectric oxide layer. The cathode of the capacitor is formed by an operating electrolyte which is usually stored in absorbent insulating foils of, for example, paper. A further aluminum foil which is the cathode foil serves as the cathode lead.
When loading such a capacitor with alternating current, heat occurs and is dissipated in the capacitor winding and to the environment by way of the housing. The heat causes overheating of the capacitor winding and, thus, greatly reduces the useful life of the device.
So as to reduce the thermal resistance between the hot winding and the housing, wound electrolyte capacitors for high alternating currents loads have an additional metallic heat bridge from the capacitor winding to the floor of the housing. This heat bridge is formed by the cathode foil which projects to the floor of the housing at one end and is thus in thermal contact with the housing. For better heat elimination, a cooling sheet can be secured to the floor of the housing and forced cooling as with water, oil or air can be utilized. The relationships which exist are described in the publication Siemens-Datenbuch 1989/90, "Aluminum-und Tantal-ElektrolytKondensatoren", at pages 31-36, Chapter 5.5, "Wechselstrombelastung". See also European Patent Application 214,788, U.S. Pat. No. 3,681,666, U.S. Pat. No. 3,670,210 and Page 39 of New Electronics of 30 Sept. 1986 article entitled "Electrolytic Capacitor Design For Extended Component Life".